YAML vs JSON: When to Use Each and How to Format Both

YAML and JSON are both data serialisation formats. They can represent the same data structures — strings, numbers, booleans, arrays, and objects. But they have different design philosophies, and the choice between them affects readability, writability, and how easily mistakes slip through.

JSON: Strict and Portable

JSON's strength is its strictness. The grammar is tiny and unambiguous. Every value type is clearly delimited: strings need double quotes, arrays have square brackets, objects have curly braces. There's no whitespace ambiguity.

This makes JSON trivial to parse reliably. Every programming language has a JSON parser built in or available as a standard library, and they all produce identical results for the same input. JSON is the right choice when data is being consumed by machines — API responses, configuration files read by programs, data storage formats.

JSON's weakness as a human-writable format: it doesn't allow comments, trailing commas cause parse errors, and all those quotes and brackets add noise when reading configuration.

YAML: Human-First

YAML is designed to be written and read by humans. It uses indentation to define structure (like Python), doesn't require quotes for strings in most cases, and supports comments with #.

# YAML version of a server config
server:
  host: example.com
  port: 8080
  tls: true
  allowed_origins:
    - https://app.example.com
    - https://admin.example.com

The same structure in JSON:

{
  "server": {
    "host": "example.com",
    "port": 8080,
    "tls": true,
    "allowed_origins": [
      "https://app.example.com",
      "https://admin.example.com"
    ]
  }
}

For long configuration files that humans write and maintain, YAML's reduced noise makes a significant difference. This is why YAML is the standard for Kubernetes configs, GitHub Actions, Ansible, Docker Compose, and most CI/CD tools.

YAML's Pitfalls

YAML's flexibility creates some famous foot-guns:

The Norway problem: in older YAML versions, the two-letter country code NO is parsed as the boolean false. YES, ON, OFF, TRUE, FALSE are all booleans. YAML 1.2 fixed most of this, but old parsers are common.

Indentation matters: mixed tabs and spaces cause parse errors. Consistently use spaces (usually 2 per level). A wrongly indented key moves it to the wrong parent — the YAML is valid, but the data is wrong.

Accidental type coercion: 1.0 is a float, 1 is an integer, true is a boolean — unless you quote them. A version number like 1.0 that you intended as a string becomes a number.

Which to Use

• API responses: JSON — it's the universal standard, no ambiguity
• Config files humans write: YAML — cleaner, supports comments
• Database storage: JSON — deterministic parsing, widely supported
• CI/CD and DevOps: YAML — industry standard (GitHub Actions, GitLab CI, Kubernetes)

Use our YAML Formatter & Validator and JSON Formatter & Validator to quickly check and clean up either format.